Zhen Gu, a professor of bioengineering at the UCLA Samueli School of Engineering who led the study, said the approach could be used in concert with other therapies, such as chemotherapy and stem cell treatment, to improve their effectiveness.

Gu said the method would have to be tested and approved in human clinical trials before it could be incorporated in treatments for people with leukaemia.

Acute myeloid leukaemia is a cancer that starts in bone marrow and can spread to the bloodstream and other parts of the body.

With a compromised immune system, a person with this type of leukaemia could die from complications from other diseases.

As a treatment for leukaemia, chemotherapy on its own is only moderately effective: Leukaemia fails to go into remission in about 1 in 3 patients following chemotherapy, according to the American Cancer Society.

About half of people with the disease who do experience remission may have a relapse, typically within two years after treatment, usually because chemotherapy cannot reach cancer cells in bone marrow.

The UCLA-led research aimed to solve that problem by devising a method to deliver medicine directly into the bone marrow.

The approach, termed “cell combination drug delivery” is the first to link two different cells together for therapeutic purposes.

In the combined cells, the blood platelets are used to deliver immunotherapy drugs called checkpoint inhibitors (the UCLA researchers used a drug called an aPD-1 antibody), which seek out cancer cells and neutralise their defences.

Once this occurs, the body’s immune system can identify and destroy the cancer cells.

“This part of the cell combination is like a delivery truck,” Gu said. “We can package medicines or immune system boosters on the cell surface of platelets, and have them activated to unload once at the target site inside the body.”

The second element of the two-cell combination is hematopoietic stem cells, or blood stem cells, which can find their way into the bone marrow through specific chemical signals.

“The hematopoietic stem cells are like a homing signal to the bone marrow,” said Quanyin Hu, a lead author of the paper and former doctoral student in Gu’s research group. “Once the stem cells guide the combo cells into the marrow, the platelets can be activated. They release immunotherapy cargoes inside the marrow to facilitate the body’s own defences, in this case T cells, to kill leukaemia cells.”

The researchers plan to continue studying the approach as a potential therapy for leukaemia and other diseases.